[PATCH] usb: core: config.c: usb_get_configuration() simplified
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From: Michal Nazarewicz on 17 Apr 2010 11:20 usb_gat_configuratio() used two pointers to point to the same memory. Code simplified, by removing one of them. Signed-off-by: Michal Nazarewicz <mina86(a)mina86.com> --- drivers/usb/core/config.c | 10 ++++------ 1 files changed, 4 insertions(+), 6 deletions(-) > On Sat, 17 Apr 2010, Michal Nazarewicz wrote: >> usb_get_configuration() uses a temporary buffer allocated on heap >> to read USB configuration descriptor. The buffer is just nine >> bytes an so it is a waste to allocate it on heap where it can be >> allocated on stack with the rest of local variables. This >> simplifies the code and minimises memory usage. Alan Stern <stern(a)rowland.harvard.edu> writes: > This is completely wrong. You are not allowed to do DMA to buffers on > the stack; some architectures are not capable of handling it. That makes sense; I haven't considered this thinking that copying nine bytes by CPU, rather then using DMA, is not a big issue. Still, the change proposed by attached commit does not suffer from DMA issue and still simplify the code. diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c index 0d3af6a..4b23e7f 100644 --- a/drivers/usb/core/config.c +++ b/drivers/usb/core/config.c @@ -722,7 +722,6 @@ int usb_get_configuration(struct usb_device *dev) int ncfg = dev->descriptor.bNumConfigurations; int result = 0; unsigned int cfgno, length; - unsigned char *buffer; unsigned char *bigbuffer; struct usb_config_descriptor *desc; @@ -751,17 +750,16 @@ int usb_get_configuration(struct usb_device *dev) if (!dev->rawdescriptors) goto err2; - buffer = kmalloc(USB_DT_CONFIG_SIZE, GFP_KERNEL); - if (!buffer) + desc = kmalloc(USB_DT_CONFIG_SIZE, GFP_KERNEL); + if (!desc) goto err2; - desc = (struct usb_config_descriptor *)buffer; result = 0; for (; cfgno < ncfg; cfgno++) { /* We grab just the first descriptor so we know how long * the whole configuration is */ result = usb_get_descriptor(dev, USB_DT_CONFIG, cfgno, - buffer, USB_DT_CONFIG_SIZE); + desc, USB_DT_CONFIG_SIZE); if (result < 0) { dev_err(ddev, "unable to read config index %d " "descriptor/%s: %d\n", cfgno, "start", result); @@ -810,7 +808,7 @@ int usb_get_configuration(struct usb_device *dev) result = 0; err: - kfree(buffer); + kfree(desc); out_not_authorized: dev->descriptor.bNumConfigurations = cfgno; err2: -- Best regards, _ _ .o. | Liege of Serenly Enlightened Majesty of o' \,=./ `o ..o | Computer Science, Michal "mina86" Nazarewicz (o o) ooo +--<mina86-tlen.pl>--<jid:mina86-jabber.org>--ooO--(_)--Ooo-- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |